1.
TIM PETTERSEN • SENIOR DEVELOPER • ATLASSIAN • @KANNONBOY
Code review
vs
Pull requests

2.
@kannonboy
Code review at Atlassian
2006
2007
Atlassian acquires
Cenqua, starts using
Crucible @kannonboy

3.
@kannonboy
2006
2007
Atlassian acquires
Cenqua, starts using
Crucible
Atlassian acquires @kannonboy

4.
@kannonboy
2007 Cenqua, starts using
Crucible
2010 Atlassian acquires
Bitbucket
2011 Work starts on “Caviar”
! @kannonboy

5.
@kannonboy
2010 Atlassian acquires
Bitbucket
2011 Work starts on “Caviar”
2012 Stash 1.0 ships
!
@kannonboy

6.
@kannonboy
2011 Work starts on “Caviar”
2012 Stash 1.0 ships
!
Stash 2.0 ships with
pull requests
Unread status
@kannonboy

7.
@kannonboy
2012 Stash 1.0 ships
Stash 2.0 ships with
pull requests
Merge checks
Comment drift
Unread status
Conflict markers
Build status integration @kannonboy

8.
@kannonboy
Stash renamed to
Bitbucket Server2015
Merge checks
Conflict markers
Build status integration
Reviewer suggestions
Branch permissions
Comment likes
Enhanced branch permissions
Iterative review
Merge strategies
Reviewer statuses @kannonboy

9.
@kannonboy
Bitbucket Server2015
Comment likes
Enhanced branch permissions
Iterative review
Merge strategies
Reviewer statuses
Today
@kannonboy

10.
@kannonboy
TYPES OF REVIEW
YOU NEED CODE REVIEW
CODE REVIEW @ ATLASSIAN
TIPS FOR TEAMS
Agenda

11.
Automated tests
@kannonboy

12.
Automated tests
@kannonboy

13.
human judgement needed
?
“what-evs”
bad API decision
O(n!) algorithm
technical debt
Automated tests
@kannonboy

14.
Code
Review
Photo: Yogi (Flickr)
@kannonboy

15.
Better
Code
Shared
Knowledge
Team
Ownership
@kannonboy

16.
G =
1
R+1
Developer guilt
@kannonboy

17.
Team
Ownership
@kannonboy

18.
Team
Ownership
@kannonboy

19.
Better
Code
Shared
Knowledge
Team
Ownership
@kannonboy

20.
Code reviews take
negative time
@kannonboy

21.
Reviews and releases
10
20
30
40
Daily Weekly Monthly Quarterly Yearly
Code Review No Code Review
Source: Atlassian Git Survey 2013
@kannonboy

22.
Types of code review
@kannonboy

23.
Pull requests
Code review
Post-commit review
Pre-commit review
master
for/master
Staging area @kannonboy

24.
Pre-commit review
master
@kannonboy

25.
Pre-commit review
dev $project-dev@example.com
master
maintainer @kannonboy

26.
// flat fees and taxes
final float customsFee = 5.5f;
final float immigrationFee = 7f;
final float federalTransportTax = .025f;
public float calculateAirfare(float baseFare) {
float fare = baseFare;
fare += immigrationFee + customsFee;
fare *=
return fare;
}
AirfareCalculator.java
federalTransportTax;
@kannonboy

27.
// flat fees and taxes
final float customsFee = 5.5f;
final float immigrationFee = 7f;
final float federalTransportTax = .025f;
public float calculateAirfare(float baseFare) {
float fare = baseFare;
fare += immigrationFee + customsFee;
fare *=
return fare;
}
(1 + )
AirfareCalculator.java
federalTransportTax ;
@kannonboy

28.
Pre-commit review
From: Tim Pettersen <tim@atlassian.com>
Date: Mon, 12 Sep 2016 10:24:10 +1000
Subject: [PATCH] Calculate federal transport tax correctly
--- a/com/atlassian/airfare/AirfareCalculator.java
+++ b/com/atlassian/airfare/AirfareCalculator.java
@@ -10,7 +10,7 @@
public float calculateAirfare(float baseFare) {
float fare = baseFare;
fare += immigrationFee + customsFee;
- fare *= federalTransportTax;
+ fare *= (1 + federalTransportTax);
return fare;
}
$ git format-patch HEAD~1 --stdout
@kannonboy

29.
Pre-commit review
dev
maintainer
public float calculateAirfare(float baseFare) {
float fare = baseFare;
fare += immigrationFee + customsFee;
- fare *= federalTransportTax;
+ fare *= (1 + federalTransportTax);
return fare;
}
Subject: [PATCH] Calculate federal transport tax correctly
@kannonboy

30.
>
>
>
>
>
The braces are unnecessary.
Pre-commit review
dev
maintainer
public float calculateAirfare(float baseFare) {
float fare = baseFare;
fare += immigrationFee + customsFee;
- fare *= federalTransportTax;
+ fare *= (1 + federalTransportTax);
return fare;
}
Subject: Re: [PATCH] Calculate federal transport tax correctly
>
>
@kannonboy

31.
>
>
>
>
>
>
>
> >
>
Technically true, but I think they add clarity.
>
>
>
>
>
>
>
The braces are unnecessary.
Pre-commit review
dev
maintainer
public float calculateAirfare(float baseFare) {
float fare = baseFare;
fare += immigrationFee + customsFee;
- fare *= federalTransportTax;
+ fare *= (1 + federalTransportTax);
return fare;
}
Subject: Re: Re: [PATCH] Calculate federal transport tax correctly
@kannonboy

32.
> > > > > > > > > > > > > > > > > > > > > > > > > > > > >
> > > > > > > > > > > > > > > > > > > > > > > > > > > > >
> > > > > > > > > > > > > > > > > > > > > > > > > > > > >
> > > > > > > > > > > > > > > > > > > > > > > > > > > > >
> > > > > > > > > > > > > > > > > > > > > > > > > > > > >
> > > > > > > > > > > > > > > > > > > > > > > > > > > > >
> > > > > > > > > > > > > > > > > > > > > > > > > > > > >
> > > > > > > > > > > > > > > > > > > > > > > > > > > > >
> > > > > > > > > > > > > > > > > > > > > > > > > > > > >
> > > > > > > > > > > > > > > > > > > > > > > > > > > > >
> > > > > > > > > > > > > > > > > > > > > > > > > > > > >
> > > > > > > > > > > > > > > > > > > > > > > > > > > > >
Pre-commit review
dev
maintainer
Subject: Re: Re: Re: Re: Re: Re: Re: Re: Re: Re: Re: Re:
@kannonboy

33.
Iteration
m
aster
@kannonboy

34.
Pre-commit review
Linus Torvalds*
Module
maintainers
File / driver
maintainers
Contributors
linux-kernel@vger.kernel.org
* Gross oversimplification,
check out: bit.ly/linux-dev
@kannonboy

35.
Pre-commit review
Junio C Hamano*
Contributors
git@vger.kernel.org
* Also an oversimplification
@kannonboy

36.
Pull requests
Post-commit review
Pre-commit review
master
for/master
Staging area
Pre-commit review
Version control agnostic
Difficult to read
High barrier to submit patches
Simple and decentralized
Difficult to iterate
Easy to keep ‘000s of people in the loop
Have to manually merge work
@kannonboy

37.
Post-commit review
@kannonboy

38.
Flexible structure
master
master
patches & untracked files
commits
branches
specific filesmultiple repos
@kannonboy

39.
Iterative review
Branch
diff
Merge
diff
Pull request diffs
@kannonboy

40.
Iterative review
Branch
diff
Post-commit review diffs
Arbitrary commit diffs
@kannonboy

41.
Iterative review in
@kannonboy

42.
Iterative review in
@kannonboy

43.
Not an SCM
SCM host
(e.g. Bitbucket)
Review host
(e.g. Crucible)
Dev team
push & pull
code review
slurp
slurp
slurp
slurp
@kannonboy

44.
Post-commit review
Post-commit review
Supports popular CVCS and DVCS
Have to manually merge work
Flexible review content
Need a separate VCS host
Easy to iterate
Hard to enforce process
@kannonboy

45.
Pull requests
master
for/master
Staging area @kannonboy

46.
Gerrit
and DIFFY
The Kung Foo
Review Cuckoo
@kannonboy

47.
Gerrit is very “Git-y”
$ git config -f ~/gerrit/etc/gerrit.config gerrit.canonicalWebUrl
http://localhost:8080/
@kannonboy

48.
Staging area review
for/master
master
reviewers approved?
verified (build passing)?
Dev team
fetch
push
@kannonboy

49.
From: Gerrit Code Review - A Quick Introduction
@kannonboy

50.
From: Gerrit Code Review - A Quick Introduction
+2
+1
0
-1
-2
@kannonboy

51.
“squash commits first”
$ git push origin HEAD:refs/for/master
# typey type type
$ git commit -am “Review feedback”
Counting objects: 2108776, done.
Delta compression using up to 8 threads.
Compressing objects: 100% (59/59), done.
Writing objects: 100% (86/86), 893.21 KiB, done.
Total 86 (delta 0), reused 0 (delta 0)
! [remote rejected] HEAD -> refs/for/master (squash commits first)
error: failed to push some refs to ‘ssh://...'
@kannonboy

52.
“squash commits first”
for/master
@kannonboy

53.
“squash commits first”
for/master
push
@kannonboy

54.
“squash commits first”
for/master
push
push --force
@kannonboy

55.
“squash commits first”
for/master
push
push --force
push --force
@kannonboy

56.
From: Gerrit Code Review - A Quick Introduction
@kannonboy

57.
Pull requests
Post-commit review
Pre-commit review
master
for/master
Staging area
Staging area review
Sophisticated policy enforcement
Steep learning curve to use & administer
Iteration is a little awkward
FOSS project built in Java, on JGit
Git only
Clean commit history
@kannonboy

58.
Pull requests
it review
@kannonboy

59.
Branches only
master
master
patches & untracked files
commits
branches
specific filesmultiple repos
@kannonboy

60.
Pull requests
review before merging
> Code review
@kannonboy

61.
Pull requests > Code review
Passing build
Reviewer sign-off
Ready for deployment
@kannonboy

62.
Pull requests > Code review
Passing build
Reviewer sign-off
Ready for deployment
@kannonboy

63.
Two developers about to
press the “Merge” button
@kannonboy

64.
Merge Strategies
@kannonboy

65.
@kannonboy

66.
--no-ff
--ff-only
--squash --ff-only
--squash
--ff
@kannonboy

67.
git merge --no-ff
@kannonboy
m
aster
feature/JIRA-123
“Always create a merge commit.”

68.
git merge --no-ff
@kannonboy
m
asterfeature/JIRA-123
“Always create a merge commit.”

69.
git merge --ff
@kannonboy
m
aster
feature/JIRA-123
“Fast forward if you can, otherwise
create a merge commit.”

70.
git merge --ff
@kannonboy
m
aster
feature/JIRA-123
“Fast forward if you can, otherwise
create a merge commit.”

71.
git merge --ff
@kannonboy
m
aster
“Fast forward if you can, otherwise
create a merge commit.”

72.
git merge --ff
@kannonboy
m
aster
“Fast forward if you can, otherwise
create a merge commit.”

73.
git merge --ff-only
@kannonboy
m
aster
feature/JIRA-123
“Only allow fast forwards.”

74.
git merge --ff-only
@kannonboy
m
aster
feature/JIRA-123
“Only allow fast forwards.”

75.
git merge --ff-only
@kannonboy
m
aster
“Only allow fast forwards.”

76.
git merge --ff-only
@kannonboy
m
aster
“Only allow fast forwards.”

77.
git merge --ff-only
@kannonboy
m
aster
“Only allow fast forwards.”

78.
git merge --ff-only
@kannonboy
m
aster
“Only allow fast forwards.”

79.
git merge --squash
@kannonboy
“Combine commits on branch into a new commit
on master.”
m
aster
feature/JIRA-123

80.
git merge --squash
@kannonboy
“Combine commits on branch into a new commit
on master.”
m
aster

81.
git merge --squash
@kannonboy
“Combine commits on branch into a new commit on master.
Fail if master has any commits that branch doesn’t.”
m
aster
--ff-only

82.
git merge --squash
@kannonboy
“Combine commits on branch into a new commit on master.
Fail if master has any commits that branch doesn’t.”
m
aster
--ff-only

83.
git merge --squash
@kannonboy
“Combine commits on branch into a new commit on master.
Fail if master has any commits that branch doesn’t.”
m
aster
--ff-only

84.
Merge Commit Fast forward Squash
Concise history
Lose context of how
features evolved
Which should I use?
“Ugly” history
Full traceability
Hard to screw up
mostly some
--no-ff --ff-only --squash
@kannonboy
No merge commits
Verbose history
Requires rebasing

85.
Pull requests
bit.ly/git-lfs
Sophisticated policy enforcement
Less flexible review content
DVCS had some limitations around file size
Choice of merge strategies
Multiple team members can author code under review
Git & Mercurial
@kannonboy

86.
pull requests
@kannonboy
Tim’s
tips for
top ten

87.
1. One issue, one pull request
= 
@kannonboy

88.
1. One issue, one pull request
# what’s shipping?
$ git branch --merged
# what’s left to ship?
$ git branch --no-merged
@kannonboy

89.
master
IN REVIEW DONEIN PROGRESSOPEN
@kannonboy
Automatic Transitions

90.
feature/JIRA-30
master
IN REVIEW DONEIN PROGRESSOPEN
Branch created!
@kannonboy
Automatic Transitions

91.
feature/JIRA-30
master
IN REVIEW DONEIN PROGRESSOPEN
Pull Request Created!
@kannonboy
Automatic Transitions

92.
feature/JIRA-30
master
IN REVIEW DONEIN PROGRESSOPEN
Pull Request Merged!
@kannonboy
Automatic Transitions

93.
2. Minimum TWO approvals before merge
@kannonboy

94.
2. Minimum TWO approvals before merge
3. Have 1.5x - 2.5x that number reviewers
@kannonboy

95.
Fewer reviewers find more defects
0
7.5
15
22.5
30
1 2 3 4 5 6 7 8 9
Defects/kLoC
Number of Reviewers
@kannonboy
source: bit.ly/review-stats

96.
More reviewers spend less time
0
7
14
21
28
1 2 3 4 5 6
Minutesspent/reviewer
Number of Reviewers
@kannonboy
source: bit.ly/review-stats

97.
4. Use blame to pick reviewers
@kannonboy

98.
4. Use blame to pick reviewers
$ npm install -g git-guilt
# find blame delta for current branch
$ git guilt `git merge-base master HEAD` HEAD
Alice Foo ++++++++++++++++++++++++(239)
Bob Bar ++++++++
Eve Baz -------
Mira Ted ----------------
Bec Opal ------------------------(-159)
@kannonboy

99.
4. Use blame to pick reviewers
bit.ly/suggest-reviewers @kannonboy

100.
4. Use blame to pick reviewers
bit.ly/suggest-reviewers @kannonboy

101.
4. Use blame to pick reviewers
bit.ly/suggest-reviewers @kannonboy

102.
5. @mention specialists
@kannonboy

103.
6. Stuck in review?
Make Tuesday & Thursday inbox zero days
@kannonboy

104.
betterCode;
7. Move comments into code
review
comments
// comments
// in code
@kannonboy

105.
8. Build a team policy, as a team…
…and enforce it! @kannonboy

106.
9. Add screenshots for UI/UX changes
(gifs / videos are even better) @kannonboy

107.
9. Add screenshots for UI/UX changes
(gifs / videos are even better) @kannonboy
Monosnap GIPHY ScreenFlow

108.
@kannonboy
Ask a programmer to review 10
lines of code, they'll find 10 issues.
Ask them to do 500 lines and
they'll say it looks good.
@GIRAYOZIL
“
”
10. Keep it concise

109.
10. Keep it conciseSecondsperline
Lines of Code
1 line per second
100 lines per second
@kannonboy
source: bit.ly/review-stats

110.
Code Review vs. Pull requests
Need to review multiple
repos at once
Not on Git
Heavily iterative workflow
Literally everyone else
Dendrophobia
+
@kannonboy
(Traditional)

111.
@kannonboy
bitbucket.org
Bitbucket
atlassian.com/crucible
Crucible
gerritcodereview.com
Gerrit
Looking
for
more?
Follow me for occasional Git &
Bitbucket trivia